Introduction
Period 5 (group 3 [IIIB] to group 12 [IIB]) is located in the second row of the transition ele- ments and represents 10 of the transition metals to nonmetals found in the periodical table of chemical elements. This period is also known to include some of the so-called rare-earth elements. Most of the rare-earths are found in the lanthanide series, which follows barium (period 6, group 3). (Check the periodic table to locate the major rare-earth elements in the lanthanide series. These are addressed in a later section of the book.)
YTTRIUM
SYMBOL: Y PERIOD: 5 GROUP: 3 (IIIB) ATOMIC NO: 39
ATOMIC MASS: 88.9059 amu VALENCE: 3 OXIDATION STATE: +3 NATURAL STATE: Solid
ORIGIN OF NAME: Yttrium was originally found with other elements in a mineral called gadolinite that was discovered in a mine near the Swedish the town of Ytterby. ISOTOPES: There are 50 isotopes of Yttrium. Only one is stable (Y-89), and it constitutes
100% of the element’s natural existence on Earth. The other isotopes range from Y-77 to Y-108 and are all produced artificially in nuclear reactions. The radioactive isotopes have half-lives ranging from 105 nanoseconds to 106.65 days.
ELECTRON CONFIGURATION
Energy Levels/Shells/Electrons Orbitals/Electrons
1-K = 2 s2
2-L = 8 s2, p6
3-M = 18 s2, p6, d10
4-N = 9 s2, p6, d1
Properties
Yttrium is always found with the rare-earth elements, and in some ways it resembles them. Although it is sometimes classified as a rare-earth element, it is listed in the periodic table as the first element in the second row (period 5) of the transition metals. It is thus also classified as the lightest in atomic weight of all the rare-earths. (Note: Yttrium is located in the periodic table just above the element lanthanum (group 3), which begins the lanthanide rare-earth series.
Yttrium dissolves in weak acids and also dissolves in strong alkalis such as potassium hydroxide. It will also decompose in water.
Yttrium’s melting point is 1,522°C, its boiling point is 5,338°C, and its density is 4.469 g/cm3.
Characteristics
Yttrium (39Y) is often confused with another element of the lanthanide series of rare Earths—Ytterbium (70Yb). Also confusing is the fact that the rare-earth elements terbium and erbium were found in the same minerals in the same quarry in Sweden. Yttrium ranks second in abundance of all 16 rare-earth, and Ytterbium ranks 10th. Yttrium is a dark silvery- gray lightweight metal that, in the form of powder or shavings, will ignite spontaneously. Therefore, it is considered a moderately active rare-earth metal.
Abundance and Source
Yttrium is the 27th most abundant element found on Earth, so it is not exactly correct to think of it as “rare”—rather just difficult to find and extract from all the other similar elements found in its minerals.
The mineral gadolinite that was discovered in a quarry near Ytterby, Sweden, was analyzed as (Ce,La,Nd,Y)2FeBe2Si2O10. Today most yttrium is recovered from the ores of the mineral monazite,which is a dark, sandy mixture of elements [(Ce,La,Th,Nd,Y)PO4] and contains about 50% rare-earths, including about 3% yttrium. The yttrium is separated from the other rare-earths first by magnetic and flotation processes, which are followed by an iron-exchange displacement process. Yttrium’s ions are combined with fluorine ions that are then reduced by using calcium metal that yields yttrium metal (3Ca + 2YF3→ 2Y + 3CaF2). This reduction process produces high-purity yttrium that can be formed into ingots, crystals, sponge, powder, and wires.
History
In 1788 Bengt Reinhold Geijer (1758–1815), a Swedish mineralogist, analyzed a new mineral that resembled thick tar of coal in a quarry near Ytterby, Sweden, which was close to Stockholm. Geijer speculated that it might contain some tungsten. In either 1789 or 1794 (both dates are given) Johan Gadolin (1760–1850), a Finnish chemist and mineralogist, analyzed this black earth mineral and found that it contained 23% silicon dioxide, 4.5% beryllium oxide, 16.5% iron oxide, and about 55.5% of a new oxide he called yttria. Most references credit Gadolin rather than Geijer with the discovery of yttrium. An interesting note is that nearly a century later, the black mineral from which Gadolin obtained the new element yttrium was named in his honor, namely “gadolinite,” and the element gadolinium is obtained from gadolinite.
Guide to the Elements | 121
In early 1828, Friedrich Wohler (1800–1882) obtained yttrium metal by reducing yttrium chloride with potassium (YCl3 + K → 2KCl + Y). He is also given credit for yttrium’s discov- ery.
Common Uses
Although yttrium metal by itself is not very useful, it has many unusual applications when combined as an alloy or as a compound with other elements. For example, when combined with iron, it is known as garnet (Y3Fe5O12), which is used as a “filter” in micro- wave communication systems. When garnets are made with aluminum instead of iron, they form semiprecious garnet gemstones (Y3Al5O12) that resemble diamonds. Aluminum garnets are referred to as “YAG” solid-state lasers because they are capable of intensifying and strengthening a single frequency of light energy that is focused through a crystal of garnet. This produces a very powerful narrow band of light waves of a single color (micro- wave frequency). YAG-type lasers have found uses in the medical industry and as a cutting tool for metals.
When combined with oxygen and europium, yttrium produces the red phosphor used as a coating in color television screens to produce the bright red color. Yttrium is also used as an alloy metal and as a high-temperature coating on iron and steel alloys. It is used as a sub- stance to deoxidize (remove the oxygen) during the production of nonferrous metals such as vanadium. Yttrium has the ability to “capture” neutrons, making it useful in the nuclear power industry. It is also used in the production of several types of semiconductors.
Examples of Compounds
Because yttrium has just one oxidation state (+3), it joins with oxygen to form yttrium oxide (2Y3+ + 3O2-→ Y
2O3), which is used to produce the red colors in TV and computer screens.
Yttrium arsenide (YAs) is used in the production of high-grade semiconductors. Since it is extremely toxic, special handling and facilities are required for its use in computer industries.
Yttrium chloride (YCl3) decomposes at the relatively low temperature of 100°C. This makes it useful as a reagent in chemical laboratories.
The compound consisting ofyttrium, copper, and barium oxide,commonly called com- pound 1-2-3, was formed in 1987 by research scientists at the universities of Alabama and Houston. It had limited superconducting capabilities. It has been known for some time that conductors of electricity such as copper resist, to some extent, the flow of electrons at normal temperatures, but at temperatures near absolute zero (zero Kelvin = –273°C), this resistance to the flow of electrons in some materials is reduced or eliminated. The 1-2-3 compound proved to be superconducting at just 93°K, which is still much too cold to be used for everyday trans- mission of electricity at normal temperatures. Research continues to explore compounds that may achieve the goal of high-temperature superconductivity.
Hazards
As a powder or in fine particles, yttrium is flammable and may spontaneously ignite in moist air. Some of its compounds, particularly those used in the semiconductor and electrical industries, are very toxic if inhaled or ingested and should only be used under proper condi- tions.
ZIRCONIUM
SYMBOL: Zr PERIOD: 5 GROUP: 4 (IVB) ATOMIC NO: 40
ATOMIC MASS: 91.224 amu VALENCE: 2, 3, and 4 OXIDATION STATE: +4 (+2 and +3
with halogens) NATURAL STATE: Solid
ORIGIN OF NAME:The name “zirconium” was derived from the Arabic word zargun, which means “gold color.” Known in biblical times, zirconium mineral had several names (e.g., jargoon, jacith, and hyacinth). Later, the mineral was called “zirconia,” and the element was later named “zirconium.”
ISOTOPES: Zirconium has 37 isotopes, ranging from Zr-79 to Zr-110. Four of them are stable, and one is a naturally radioactive isotope, with a very long half-life. All five con- tribute to the element’s natural existence on Earth. The stable isotopes are the following: Zr-90 = 1.45%, Zr-91 = 11.22%, Zr-92 = 17.15%, and Zr-94 = 17.38%. The one natu-
ral radioactive isotope is considered stable: Zr-96, with a half-life of 2.2 × 10+19 years,
contributes 2.80% to zirconium’s total existence on Earth. All of the other isotopes are artificially radioactive and are produced in nuclear reactors or particle accelerators. They
have half-lives ranging from 150 nanoseconds to 1.53 × 10+6 years.
ELECTRON CONFIGURATION
Energy Levels/Shells/Electrons Orbitals/Electrons
1-K = 2 s2 2-L = 8 s2, p6 3-M = 18 s2, p6, d10 4-N = 10 s2, p6, d2 5-O = 2 s2 Properties
Zirconium can be a shiny grayish crystal-like hard metal that is strong, ductile, and mal- leable, or it can be produced as an undifferentiated powder. It is reactive in its pure form. Therefore, it is only found in compounds combined with other elements—mostly oxygen. Zirconium-40 has many of the same properties and characteristics as does hafnium-72, which is located just below zirconium in group 4 of the periodic table. In fact, they are more similar than any other pairs of elements in that their ions have the same charge (+4) and are of the same general size. Because zirconium is more abundant and its chemistry is better known than hafnium’s, scientists extrapolate zirconium’s properties for information about hafnium. This also means that one “twin” contaminates the other, and this makes them difficult to separate.
Guide to the Elements | 123
Zirconium’s melting point is 1,852°C, its boiling point is 4,377°C, and its density is 6.506 g/cm3.
Characteristics
Zirconium is insoluble in water and cold acids. Although it is a reactive element, it resists corrosion because of its rapid reaction with oxygen, which produces a protective film of zirco- nium oxide (ZrO2) that protects any metal with which it is coated. Zirconium is best known as the gemstone zircon. Although there are different types of zircons, the most recognized is the hard, clear, transparent zircon crystal that has a very high index of refraction, which means it can bend light at great angles. These zircon crystals (zirconium sulfate, ZrSiO4) are cut with facets to resemble diamonds.
Another characteristic that makes zirconium useful is the production of “zircaloy,” which does not absorb neutrons as does stainless steel in nuclear reactors. Thus, it is ideal to make nuclear fuel tubes and reactor containers. Zircaloy is the blend (alloy) of zirconium and any of several corrosion resistant metals.
Abundance and Source
Zirconium is not a rare element. It is found over most of Earth’s crust and is the 18th most abundant element, but it is not found as a free metal in nature.
It is found in the ores baddeleyite (also known as zirconia) and in the oxides of zircons, elpidite, and eudialyte.
History
Several minerals containing zirconium were known in ancient times, one of which, jacinth, is mentioned several times in the Bible. It was not until 1789 that Martin Heinrich Klaproth (1743–1817), a German analytical chemist who also discovered uranium, identified zirconium after many others before him had failed. Klaproth analyzed the mineral jargoon (ZnSiO4), as did other scientists, and found that it contained 25% silica, 5% iron oxide, and 70% zirconia. The other scientists confused zirconia with alumina (aluminum oxide, Al2O3). Klaproth used more refined techniques and correctly identified the element zirconium.
Zirconium was isolated from other compounds in 1824 by Baron Jöns Jacob Berzelius (1779–1848), a Swedish chemist, but it was not produced in pure form until 1914 because of the difficulty in separating it from hafnium.
Common Uses
About 90% of all the zirconium produced in the United States is used in the nuclear electrical power industry. Since it does not readily absorb neutrons, it is a desired metal in the manufacture of nuclear reactors and their fuel tubes, but it must be free of its “twin” hafnium for these purposes. Zirconium is also used as an alloy with steel to make surgical instruments.
Zirconium dioxide (ZrO2) as an abrasive is used to make grinding wheels and special sandpaper. It is also used in ceramic glazes, in enamels, and for lining furnaces and high- temperature molds. It resists corrosion at high temperatures, making it ideal for crucibles and other types of laboratory ware. ZrO2 is used as a “getter” to remove the last trace of air when producing vacuum tubes.
As mentioned, zircon (ZrSiO4) has many forms, but the most used is the transparent crystal that is cut to resemble a diamond. There is even one form of zirconium used in medicine: zirconi- um carbonate (3ZrO2•CO2•H2O), which, as a lotion, can be used to treat poison ivy infections. When zirconium is alloyed with niobium, it becomes superconductive to electricity at temperatures near absolute zero Kelvin (–273°C).
Examples of Compounds
Zirconium’s common oxidation state is +4, but when combined with chlorine and other halogens, it can exist in +2 and +3 oxidation states, as follows:
Zirconium dichloride: Zr2+ + 2Cl1-→ ZrCl 2. Zirconium trichloride: Zr3+ + 3Cl1-→ ZrCl 3. Zorconium tetrachloride: Zr4+ + 4Cl1- → ZrCl 4.
Zirconium oxide (ZrO2) is the most common compound of zirconium found in nature. It has many uses, including the production of heat-resistant fabrics and high-temperature elec- trodes and tools, as well as in the treatment of skin diseases. The mineral baddeleyite (known as zirconia or ZrO2) is the natural form of zirconium oxide and isused to produce metallic zirconium by the use of the Kroll process. The Kroll process is used to produce titanium metal as well as zirconium. The metals, in the form of metallic tetrachlorides, are reduced with mag- nesium metal and then heated to “red-hot” under normal pressure in the presence of a blanket of inert gas such as helium or argon.
Zirconium carbide (ZrC) is used for light bulb filaments, for cladding metals to protect them from corrosion, in making adhesives, and as a high-temperature lining for refractory furnaces.
Zirconium sulfate [Zr(SO4)2] is an ingredient in lubricants that do not disintegrate at high- temperatures. It is also used for tanning leather to make it white and as a chemical reagent and catalyst in chemical laboratories.
Zirconium-95 is the most important of the artificial radioactive isotopes of zirconium. It is placed in pipelines to trace the flow of oil and other fluids as they flow through the pipes. It is also used as a catalyst in petroleum-cracking plants that produce petroleum products from crude oil.
Zirconium carbonate (3ZrO2•CO2•H2O), when used as an additive to lotion, is an effective treatment for skin exposed to poison ivy.
Zirconium silicate (ZrSiO4) is one form of the mineral whose crystals when polished are known as cubic zircons, which resemble diamond gemstones.
Hazards
There is disagreement relative to the dangers of the elemental form of zirconium. Some say that the metal and gemstone forms are harmless, but there is some evidence that the vapors and powder forms of the metal may be carcinogenic. Also, several zirconium compounds can pro- duce allergic reactions in humans and have proven to be toxic to the skin or lungs if inhaled.
The fine powder and dust of zirconium are explosive, especially in the presence of nonmet- als that oxidize these forms of zirconium.
NIOBIUM
SYMBOL: Nb PERIOD: 5 GROUP: 5 (VB) ATOMIC NO: 41
ATOMIC MASS: 92.906 amu VALENCE: 3 and 5 OXIDATION STATE: +3 and +5 (also
Guide to the Elements | 125
ORIGIN OF NAME:Niobium is named after the Greek mythological figure Niobe who was
the daughter of Tantalus.Tantalus was a Greek god whose name is the source of the
word “tantalize,” which implies torture: he cut up his son to make soup for other gods. ISOTOPES: There are 49 isotopes of niobium, ranging from Nb-81 to Nb-113. All are radio-
active and made artificially except niobium-93, which is stable and makes up all of the element’s natural existence in the Earth’s crust.
ELECTRON CONFIGURATION
Energy Levels/Shells/Electrons Orbitals/Electrons
1-K = 2 s2 2-L = 8 s2, p6 3-M = 18 s2, p6, d10 4-N = 12 s2, p6, d4 5-O = 1 s1 Properties
Niobium is a soft grayish-silvery metal that resembles fresh-cut steel. It is usually found in minerals with other related metals. It neither tarnishes nor oxidizes in air at room tempera- ture because of a thin coating of niobium oxide. It does readily oxidize at high temperatures (above 200°C), particularly with oxygen and halogens (group 17). When alloyed with tin and aluminum, niobium has the property of superconductivity at 9.25 Kelvin degrees.
Its melting point is 2,468°C, its boiling point is 4,742°C, and its density is 8.57 g/cm3.
Characteristics
Some of niobium’s characteristics and properties resemble several other neighboring ele- ments on the periodic table, making them, as well as niobium, difficult to identify. This is particularly true for tantalum, which is located just below niobium on the periodic table.
Niobium is not attacked by cold acids but is very reactive with several hot acids such as hydrochloric, sulfuric, nitric, and phosphoric acids. It is ductile (can be drawn into wires through a die) and malleable, which means it can be worked into different forms.
Abundance and Source
Niobium is the 33rd most abundant element in the Earth’s crust and is considered rare. It does not exist as a free elemental metal in nature. Rather, it is found primarily in sev- eral mineral ores known as columbite (Fe, Mn, Mg, and Nb with Ta) and pyrochlore [(Ca, Na)2Nb2O6 (O, OH, F)]. These ores are found in Canada and Brazil. Niobium and tantalum [(Fe, Mn)(Ta, Nb)2O6] are also products from tin mines in Malaysia and Nigeria. Niobium
is a chemical “cousin” of tantalum and was originally purified by its separation through the process known as fractional crystallization (separation is accomplished as a result of the differ- ent rates at which some elements crystallize) or by being dissolved in special solvents. Today most of the niobium metal is obtained from columbite and pyrochlore through a complicated refining process that ends with the production of niobium metal by electrolysis of molten niobium potassium fluoride (K2NbF7).
History
Niobium has a rather confusing history, starting in 1734 when the first governor of Connecticut, John Winthrop the Younger (1681–1747), discovered a new mineral in the iron mines of the New England. He named this new mineral “columbite.” Although he did not know what elements the mineral contained, he believed it contained a new and as yet unidentified element. Hence, he sent a sample to the British Museum in London for analysis. It seems that the delivery was mislaid and forgotten for many years until Charles Hatchett (1765–1847) found the old sample and determined that, indeed, a new element was pres- ent. Hatchett was unable to isolate this new element that he named columbium, which was derived from the name of Winthrop’s mineral.
The story became more complicated when in 1809 the English scientist William Hyde Wollaston (1766–1828) analyzed the sample mineral and declared that columbium was